The Central Limit Theorem tells us that adding together independent noise sources will eventually give us gaussian noise. Twelve is certainly enough for auditory purposes.

x ={{WhiteNoise.ar}.dup(12).mean.dup*0.5}.play;
x.free;

In the book, Andy says that it is more efficient to use two white noise sources and to create a gaussian shape using the Box-Muller transform. However, this involves some relatively heavy mathematical operations (log, cos, sqrt) so it's not actually obvious which approach is more efficient on a given system. Compare the CPU usage (and the audio result) of the above, with the following: